The iPhone 6 Plus is part of the iPhone line, succeeding the iPhone 5s. Apple held an event to formally introduce the phone (and its little brother, the iPhone 6) on September 9, 2014. Notable features include a new 5.5" Retina HD display, an updated body styling that is .5 mm thinner than the 5s, and NFC capability for Apple's new mobile payment system Apple Pay. The iPhone 6 Plus also features expanded fitness tracking abilities with a new fitness-tracking application powered by the updated M8 motion coprocessor and a barometer used to sense elevation.